This invention relates to a method and apparatus for operating a variable speed power generation system and more particularly to a method and apparatus for operating a variable speed power generation system of the type which is suitable for regulating the generated output or power of an induction generator by controlling current in the secondary side of the generator coupled to a prime mover.
Conventionally, as described in Electric Engineering Handbook published by the Institute of Electrical Engineers of Japan, Tokyo, Japan, in Apr., 1978, pp. 1108 to 1109, the power generation system employs a governor which controls the output of the prime mover. More particularly, it has been the practice that when the load remains unchanged, the water wheel is operated at a prescribed rotation speed, but when the load is changed and unbalanced with the water wheel output to change the rotation speed, the change in the rotation speed is detected and the governor is operated in accordance with this change to control the flow rate for the water wheel, whereby the amount of power generation of the synchronous generator can be so controlled as to maintain the prescribed rotation speed. However, the governor used for controlling power in the conventional power generation system is required to have a complicated control mechanism and its maintenance and inspection is time-consuming. In addition, the governor can not achieve highly efficient power control without difficulties.
Another method of operating generators with high efficiencies is described in JP-A-62-118068, according to which torque of a generator is controlled on the basis of the rotation speed and generated output of the generator. This control method, however, could not be properly applied without changes to the system which efficiently controls the generated output of a wound-rotor induction generator by controlling current in the secondary side of the generator coupled to the water wheel.